The present invention relates to a dust seal for optical devices and, more particularly, polyolefin tubing used to encompass, and thus, seal optical devices.
Optical devices are well known in the art and process light and the images represented in light. One type of optical device is known as an optical scanning device. An optical scanning device generates machine-readable image data (sometimes referred to herein simply as image data) representative of an image of the object. Generating image data representative of an image of the object is sometimes referred to as imaging or scanning the object. The image data generated by the optical scanning device may, as an example, be in the form of binary numbers and stored in a data storage device for processing. The following patents which describe optical scanning devices are all hereby incorporated by reference for all that is disclosed therein: U.S. Pat. No. 5,552,597 of McConica for HAND-HELD SCANNER HAVING ADJUSTABLE LIGHT PATH; U.S. Pat. No. 5,646,394 of Steinle for IMAGING DEVICE WITH BEAM STEERING CAPABILITY; and U.S. Pat. No. 5,646,402 of Khovaylo et al. for EXPANDABLE HAND-HELD SCANNING DEVICE.
Some optical scanning devices employ line-focus systems, which image an object by sequentially focusing narrow xe2x80x9cscan linexe2x80x9d portions of the object onto a linear photosensor array as the optical scanning device is moved relative to the object. Scanning the object is performed by illuminating the object and focusing a narrow scan line portion of the light reflected from the object onto the photosensor array. As the object is moved relative to the optical scanning device, a plurality of scan line images are formed, which taken collectively, represent an image of the object.
A linear photosensor array generally consists of a linear array of photodetector elements (sometimes referred to herein simply as photodetectors), which image small area portions of the scan line. These small area portions of the scan line are commonly referred to as xe2x80x9cpicture elementsxe2x80x9d or xe2x80x9cpixels.xe2x80x9d In a contact image sensor-type optical scanning device, there are typically between 300 and 600 photodetectors per inch in the linear array. In a scanning device using a charge-coupled device, there are typically between 1,500 and 2,000 photodetectors per inch in the linear array.
In response to light from its corresponding pixel location on the scan line, each photodetector in the linear photosensor array produces image data which is representative of the light it experiences during an interval of time known as a sampling interval. The image data may, as an example, be in the form of voltages that correspond to the intensity of light received by the photodetectors. For example, a photodetector that receives a relatively high intensity of light may output a relatively high voltage and a photodetector that receives a relatively low intensity of light may output a relatively low voltage. The image data generated by the photodetectors may be received and processed by an appropriate data processing system. Light-colored sections of the object tend to reflect relatively high intensities of light and dark-colored sections of the object tend to reflect relatively low intensities of light. Thus, the photodetectors imaging light-colored sections of the object will receive relatively high intensities of light and will, accordingly, output relatively high image data values representative of the relatively high intensities of light. Photodetectors imaging dark-colored sections will receive relatively low intensities of light and will, accordingly, output relatively low image data values representative of the relatively low intensities of light.
Some optical scanning devices are calibrated to establish a correlation between the image data values and the intensity of light reflecting from the object being imaged. For example, during calibration, the scanning device may image a surface having a predetermined and uniform reflectivity. Under ideal conditions, the image data generated by all of the photodetectors should be a predetermined and uniform value. Due to inconsistencies in the manufacture of the photodetectors, however, the image data values generated by the photodetectors will vary between photodetectors. The calibration process overcomes this problem by scaling the image data values from each photodetector so that the image data values all have the same predetermined value. The scaling factor for each photodetector is stored by the scanning device and used to accurately replicate the image of the object.
The components comprising the optical scanning device are typically enclosed in a sealed housing. The housing has an aperture formed therein that serves to allow light representing an image of the object being scanned to enter the housing. A transparent pane is positioned in the aperture and serves to keep contaminants from entering the housing. The transparent pane may, as an example, be a lens that is used to focus an image of the scan line portion of the object onto the photosensor array. Accordingly, the image of the object being scanned is passed through the aperture and to the photosensor array. In many optical scanning devices, the light path is directed to the photosensor array by the use of other optical components, such as additional lenses and mirrors.
If the light path between the object and the linear photosensor array intersects a contaminant, the contaminant will block the light path and will, thus, corrupt the image data. More specifically, the contaminant will block the light path between a pixel area of the scan line and its corresponding photodetector. Depending on the size of the photodetectors and the contaminant, the contaminant may partially or completely block the light path between a pixel area of the scan line and its corresponding photodetector. For example, if a dust particle is located on a mirror, lens, or photodetector, it will block the light path. This results in the section of the scan line corresponding to the location of the dust particle being imaged as though it is darker than the surface of the object. As the optical scanning device is moved relative to the object and a plurality of scan line portions of the image of the object are generated, all the scan line images will have the above-described darker area caused by the contaminant. When the image of the object is replicated, the darker area on the plurality of scan lines will appear as a dark line on the replicated image. Accordingly each contaminant in the light path may result in a separate dark line on the replicated image of the object.
The contaminant problem may also cause light-colored lines to appear on the replicated image of the object. If a contaminant blocks the light path or partially blocks the light path during the calibration process, the scanning device will recognize the photodetectors corresponding to the contaminant as photodetectors that inherently output low image data values. Accordingly, the scanning device will scale up the values of the image data output by these photodetectors. If the contaminant moves from the light path subsequent to calibration, the corresponding photodetectors will receive more light and will output higher image data values. This results in the replicated image of the object having areas that are lighter than the actual image of the object.
The contaminant problem is exacerbated as the size of the photodetectors decreases. Smaller photodetectors are used to generate a more precise image of the object and are increasingly being used in scanning devices. These smaller photodetectors, however, are more susceptible to contamination because smaller contaminants can block the light path between the object and the smaller photodetectors. Furthermore, a single contaminant may block the light to several of the smaller photodetectors.
Some optical scanning devices overcome the problems associated with contaminants by locating the components comprising the optical scanning device in a sealed housing. Locating the components in a sealed housing however, presents some problems. All of the components being located in the housing must be free of contaminants, otherwise, the contaminants may move from the components to positions where they block the light path as described above. In addition, the entire optical scanning device must be assembled in a contaminant free area, sometimes referred to as a, xe2x80x9cclean room.xe2x80x9d Otherwise, contaminants will likely enter the housing during the assembly process and cause the above-described problems. Likewise, the optical scanning device needs to be placed into a clean room if the housing is ever opened, such as for maintenance and repair service.
Portable optical scanning devices, such as hand-held scanning devices, present additional contaminant problems with regard to their power sources. Most portable optical scanning devices are powered by batteries, which, for ease of use, are typically located in a battery compartment within the housing. Unless the battery compartment is sealed, the process of exchanging the batteries subjects the internal portions of the housing to contamination. This, in turn, subjects the optical components to contamination. Some portable optical scanning devices overcome this problem by providing a separate seal for the battery compartment. Providing a separate seal for the battery compartment, however, tends to increase the cost of the optical scanning device.
Accordingly, a need exists for a device in which contaminants are prevented from interfering with the optical components associated with an optical device.
A sheath for reducing the probability of contaminants entering an optical device is disclosed herein. The optical device may be of the type having a base portion and a substrate separated by a space wherein the base portion and the substrate are substantially planar and parallel. Optical components may be located in the space between the base portion and the substrate. The sheath may be in the form of a heat shrink material, such as polyolefin tubing, that may encompass the space and may be adjacent the base portion and the substrate. The heat shrink material may then be heated so as to resiliently engage the base portion and the substrate. Thus, the heat shrink material serves as a barrier to contaminants and substantially reduces the probability that contaminants may enter the optical device.